Once an egg has been laid by an animal, it must undergo a period of incubation, either naturally or artificially, during which time development of the young animal takes place. Many birds for example, sit on an egg or clutch of eggs in order to regulate temperature and humidity around the egg(s), such regulation being crucial for the survival and proper development of the embryo inside each egg. Other animals utilise different sources, for example solar or geothermal energy, for this purpose. Alternatively, incubation may be carried out and/or assisted by man. Man-made incubators are well known that can hold a number of eggs and which provide artificial temperature and humidity regulation of the air around the eggs.
Many breeders and conservationists of egg-laying animals need to know whether or not the embryo is alive and developing at the proper rate inside the egg. Such knowledge is required throughout the incubation period, and is important both in natural and artificial incubation scenarios in order to maximise the chances of survival of the young. In natural incubation, for example a clutch of eggs brooded by a bird, if one or more embryos does not survive, those eggs can become infected by bacteria and endanger the remaining eggs. Furthermore, some species of parrot for example the Palm Cockatoo, Black Cockatoo and Hyacinthine Macaw, can only lay fertile eggs during a short period of time each year and even then only incubate one egg at a time. If that egg does not survive, the opportunity for successful breeding has been missed for that year. Such scenarios can have serious implications for endangered species, and for breeders and keepers of such birds who exchange them for considerable sums of money. The situation is analogous for many species of egg-laying animal.
At present there are two well known methods for checking the fertility and development of eggs. The first method, known as “candling”, involves placing an egg in front of an intense light source, for example tungsten halogen, so that the inside of the egg is visible to the naked eye, and looking for signs of growth e.g. vein development that is first visible after approximately four days in parrot eggs. Over the next few days it is possible to check for further growth by looking for increasing numbers and density of veins and a growing “dark spot” in the centre of the egg. However, there are three disadvantages with “candling”, the first being that a high intensity of light is required to see into the egg meaning that it is exposed to high temperature levels that can damage or kill the embryo in the egg if held over the light for too long. Secondly, the “dark spot” grows at such a rate that after approximately twelve days (in parrot eggs) it occupies so much of the volume of the egg that the veins are no longer visible and it is not possible to tell whether or not the young bird is alive. Thirdly, some eggs are not suitable for “candling” such as raptors, falcons, ducks and wild fowl, whose eggs range from dark green to dark brown in colour, and other species whose shells are so dense that the light from the lamp cannot pass through them. For such eggs it is not possible to tell whether or not they are fertile and alive in the first few days.
The second known method addresses the second and third problems mentioned above. This method involves floating the egg in still warm water and waiting for the egg to move as a result of movement of the young animal inside. There are two disadvantages associated with this method, the first being that the method is unreliable and slow since it relies on a parameter that is inherently random. Secondly, immersing the egg in water exposes it to bacteria that can pass through the shell, particularly as the egg is withdrawn from the water, when water on the surface of the egg tends to be “sucked” in through the pores of the shell severely reducing the egg's ability to self-regulate humidity. Once inside the shell the bacteria and water are in an ideal environment at 37.degree. C. to multiply, potentially endangering the life of the young animal.
U.S. Pat. No. 5,745,228 discloses an apparatus for distinguishing live from infertile poultry eggs at high speed in the presence of ambient (or background) light. The apparatus comprises a photoemitter for emitting infra-red radiation located directly opposite a photodetector. In use eggs pass at high speed (10 inches per second is suggested) between the photoemitter and photodetector on a conveyor. The photodetector is turned on and off 100 times per second in bursts of 250 .mu·s. The photodetector takes readings when the photoemitter is actuated and when deactivated; by subtracting these readings the effects of ambient light on the signal are reduced. The apparatus only has sufficient resolution to classify eggs into three groups namely, clear or early dead, mid dead, and live. These results are not significantly better than can be obtained by the aforementioned method of candling.
FR 2 455 282 discloses an improved candling method in which infra red light is passed through an egg in the presence of background light. Light having passed through the detector is detected and the output signal displayed on a visual display screen. The viability of the egg is determined by comparison of the relative intensity of the received signal either visually or automatically.
However, the disadvantage with the aforementioned publications is that only differences in the received intensity of light from each egg can be compared in order to make an assessment of the viability of an egg.
Thus, it is apparent that there is a need for an apparatus and method of testing the viability of eggs that is more reliable, that minimises the risks to which prior methods have exposed eggs, and which facilitates maximisation of the chances of survival of fertile eggs.